Colorectal cancer screening

March is colorectal cancer (CRC) awareness month. It is opportune for us to take this time to reflect on the current situation of CRC in Singapore. Colorectal cancer is the second most common cancer and the second leading cause of cancer-related mortality in Singapore.[1] The majority of CRC cases are sporadic without underlying predisposition apart from age, while approximately 20% are associated with familial clustering and approximately 5% are due to predisposing hereditary CRC syndromes.[2] According to the National Comprehensive Cancer Network Guidelines for CRC screening, individuals at average risk of developing CRC are those aged >45 years, with no personal history of colorectal neoplasia, inflammatory bowel disease, high-risk CRC genetic syndromes, cystic fibrosis or childhood cancer, and with a negative family history of colorectal neoplasia. In the presence of such personal or family history, the individual would be considered at an increased risk of CRC.[3] Western guidelines have adopted an age cutoff of 45 years for CRC screening,[2] due to the observation of increased incidence of young-onset CRC, and mathematical modelling that demonstrated that it is cost-effective to lower the age of CRC screening from 50 to 45 years for those at average risk in their healthcare settings.[4] In Singapore the age cutoff currently remains at 50 years.[5]

Patients with localised CRC have a five-year survival rate of 91%, but in the presence of regional and distant disease, the survival rate decreases to 73% and 14%, respectively.[3] Most CRCs develop through the adenoma–carcinoma sequence, and this creates opportunities to prevent cancer by removing the premalignant lesions and to diagnose CRC in its early curable stages. The cost-effectiveness of CRC screening has been clearly demonstrated,[6] and colonoscopy with polypectomy has been shown to reduce the incidence of CRC and CRC-related mortality.[7] For individuals at average risk of CRC, screening options include faecal immunohistochemical test (FIT) and colonoscopy. In Singapore, under the Screen for Life programme, subsidised screening for CRC is based on yearly FIT. Individuals with positive FIT results are eligible for subsidised colonoscopy at accredited CRC screening centres. On the other hand, individuals at increased risk for CRC should undergo colonoscopy directly. Although computed tomography colonography (CTC) is often used as an alternative for individuals not keen to undergo diagnostic evaluation by colonoscopy, it must be noted that the diagnostic yield of CTC is significantly lower than that of colonoscopy for small polyps. A systematic review with meta-analysis reported the following pooled per-polyp sensitivity for polyps — ≥10 mm: 0.81 (95% confidence interval [CI] 0.76–0.85), 6–9 mm: 0.62 (95% CI 0.58–0.67), and ≤5 mm: 0.43 (95% CI 0.39–0.47). The sensitivity of CTC for detection of polyps increased as the polyp size increased.[8]

Despite ongoing efforts in CRC screening, CRC is often diagnosed at an advanced stage, and some patients may even present with malignant large bowel obstruction, necessitating urgent decompression.[9] A local study evaluated the impact of opportunistic CRC screening using FIT kits provided by the Singapore Cancer Society. A total of 20,989 participants received 41,978 kits. However, compliance was only 38.9%, with 8156 participants returning at least one kit. Of the 8% of participants who tested positive, only 75% agreed to undergo further diagnostic investigations.[10] In addition, although colonoscopy is regarded as the gold standard test for the diagnosis of CRC, interval-type post-colonoscopy CRC (PCCRC), which is defined as CRC diagnosed after a negative colonoscopy before the next recommended surveillance interval, can occur. Baile-Maxía et al.[11] reported the occurrence of PCCRC in 4.1% of their study population. Previous inadequate bowel preparation and piecemeal polypectomy were independently associated with PCCRC.[11] Such findings highlight the possibility of missed adenomatous lesions or CRC due to inadequate bowel preparation and remnant adenoma after incomplete endoscopic resection, with subsequent disease progression.

To improve CRC outcomes, it is important to improve compliance to CRC screening. The ongoing efforts of the Health Promotion Board, Singapore Cancer Society and individual healthcare professionals to promote CRC screening are to be lauded. While annual FIT is applicable for the average-risk individuals, those at higher risk should undergo screening/surveillance colonoscopy at the appropriate time intervals.[2,3] Whether colonoscopy is performed as a screening procedure or following a positive FIT result, it is crucial to prioritise procedural quality. This includes ensuring good bowel preparation, adequate time for careful, meticulous examination of the mucosa surface, including exposing areas hidden by folds, and harnessing technology that has been shown to improve adenoma detection rate when these resources, such as artificial intelligence, image enhanced endoscopy and distal attachment devices, are available.[12] Endoscopic resection, be it standard polypectomy, endoscopic mucosal resection, endoscopic submucosal dissection or endoscopic full-thickness resection, has the potential to achieve curative outcomes for adenomas and intramucosal carcinoma. Meticulous application of these techniques is important for ensuring complete resection with no remnant disease, which will then reduce the need for salvage interventions.

Currently, there is increasing awareness of the potential impact of endoscopy on climate change due to its carbon footprint,[13] with ongoing debate about whether the volume of endoscopic procedures should be reduced. It is noteworthy that a recent study reported that screening colonoscopy could in fact reduce greenhouse gas (GHG) emissions in the long term. When CRC is diagnosed at an earlier stage, the resources needed for treatment and the number of clinic visits required will be reduced. This reduces cancer-related GHG emissions and minimises the environmental impact of cancer treatment.[14] Hence, it is not simply about doing fewer procedures that may inadvertently limit patient access to appropriate clinical services, but more about improving the quality of the procedures that need to be performed. This will in turn reduce the need for avoidable repeat procedures and the associated carbon footprint.

Whether we practice in the primary or tertiary care setting, we can all play an important role in improving clinical outcomes in CRC management. This is through health promotion, early detection by screening and appropriate timely treatment.